I've been gardening indoor and out for 25 years, and I'm really stumped on this one so thought I'd see if anyone else has had the same experience.

I've branched out to cacti and am growing some from seed. I'd been told that commercial cactus soil often contains too much peat, so I mixed up some soil based on recipes from the internet: 30% commercial cactus soil, 30% perlite, 20% limestone screenings passed through 2 mm mesh, and 20% screened compost/worm castings. After mixing the damp soil was crumbly and wouldn't hold together.

I sterilized the soil in a 425 deg oven for an hour, then moistened it, put it in an 8" clay pots and ran about a gallon of water through it, then planted my seedlings.

My problem is, every time I water it just pools on the surface. After about 15 minutes a centimetre of water will be absorbed. Even when the soil is damp it still takes forever to drain, much longer than my "regular" container soils.

What did I do wrong?! and how can I fix it without transplanting my seedlings again?